What is the difference between signed and unsigned variables?

Question

I have seen these mentioned in the context of C and C++, but what is the difference between signed and unsigned variables?

Answer 1

Unsigned variables can only be positive numbers, because they lack the ability to indicate that they are negative.

This ability is called the 'sign' or 'signing bit'.

A side effect is that without a signing bit, they have one more bit that can be used to represent the number, doubling the maximum number it can represent.